The proposed investigation will concern itself with the structure and function of an intercellular junction, the gap junction, isolated from mammalian heart and liver. The isolated junctions will be studied by electronmicroscopy, x-ray diffraction, SDS-polyacrylamide gel electrophoresis and chromatography, amino acid analysis and sequence, and thin-sections. Intact junctions in the tissues will be studied in preparations which permit the splitting of the junctions with hypertonic disaccharides. The molecular biology of membrane fusion will be studied in a model system using studies of mating in the alga, Chlamydomonas reinhardii. These studies will center around a morphological description of the mating events necessary for cell fusion, using temperature-sensitive mutants, protein isolation and fractionation, and correlated electronmicroscopy BIBLIOGRAPHIC REFERENCES: Goodenough, D.A. 1976 In vitro formation of gap junction vesicles. J. Cell Biol. 68: 220-231. Goodenough, D.A. 1976 The structure and permeability of isolated hepatocyte gap junctions. Cold Spring Harbor Symp. Quant. Biol. XL pp 37-43.